The subject matter of the invention is a device for controlling the vacuum in a vacuum line system, especially for milking installations.
A device of this kind is known, having a casing which can be attached to a vacuum line by means of a pipe connection, and in which there is disposed a main valve means comprising a main valve chamber having a valve seat on its side facing the pipe connection and air inlet apertures in its outer walls, and having a main valve connected by a stem to a membrane by which the main valve chamber is separated from a control chamber. A vacuum which depends on the vacuum prevailing in the vacuum line can be applied to the control chamber, the position of the main valve with respect to its seat being dependent upon the vacuum in the control chamber. In the casing there is disposed an auxiliary valve means influencing the vacuum in the control chamber, and having an auxiliary valve which is connected to an auxiliary membrane separating two auxiliary chambers, a first of which is connected to the vacuum line and a second to the exterior, the pressure difference thus created producing a force lifting the auxiliary valve away from an auxiliary valve seat against the adjustable force of a coil spring.
A device of this kind is described, for example, in German Auslegeschrift No. 2,363,125.
Such devices are intended for the purpose of maintaining a certain given pressure constant in vacuum line systems, and especially to keep it from decreasing. This is very important especially in milking installations. The use of the device of the invention, however, is not limited to milking installations, and can also be used for the control of vacuum in any kind of vacuum line system.
The known device has the disadvantage that the closing force applied to the main valve is determined in part by a loading weight, so that the operation of the device depends to a great extent on the position in which it is installed. In another embodiment of the known device, the main valve closing force is determined in part by a coil spring, so that the opening and closing action of the main valve is greatly dependent upon the characteristic and bias of this coil spring, so that, in the case of a linear characteristic, for example, the forces required for opening increase greatly as the opening travel increases. This had a disadvantageous effect on the regulating action of the device. Furthermore, in the known device the transmission of the reference vacuum to the first auxiliary chamber of the auxiliary valve takes place through an independent conduit running outside of the device and leading into the vacuum line at a point different from the point at which the device is connected to the vacuum line. In the first place, therefore, two places must be provided for connecting the device to the vacuum line, and secondly the reference vacuum is taken from the vacuum line at a point whose distance from the point at which the regulation takes place is not negligible under certain circumstances, and this can also result in disturbances in the regulation.